> On Jun 23, 2017, at 9:13 PM, David Baraff via swift-users
> <swift-users@swift.org> wrote:
>
> I realize this is slightly centric to iOS, but it irks me that both Apple’s
> crash report logs and popular platforms like PLCrashReporter can do the hard
> stuff like give you a stack trace, but are *completely* unable to display the
> error message from terminating a program via fatalError(), or the error
> message from, e.g. dying with a bad optional.
>
> Is there *any* to intercept the error messages that from fatalError() and
> similar like things in swift (bad optionals, invalid array accesses,
> assertions)? I would think that some sort of a “hook” into these standard
> error routines would be a good thing.
>
> In my case, if I could simply save that darn error string in a file, i could
> pick it up when the app next launches and report it along with the rest of
> the info like the stack/signal, etc.
>
> I’ve been looking through the code in stdlib/public/runtime/Errors.cpp but
> haven’t found anything promising that lets me jump in there. In my code, I’m
> likely to write things like
> guard let x = … else {
> fatalError(“Data type has payload <T> but is hooked to UI
> control with intrinsic type <U>”)
> }
>
> and having that exact string tells me precisely what’s going, far simpler
> than a stack trace.
Fatal error messages already get logged three ways:
- Printed to the process's stderr;
- Logged to the system log using asl_log;
- Set as the crash reason for CrashReporter.
The crash messages should thus already be in your crash reports somewhere. See
https://github.com/jckarter/swift/blob/master/stdlib/public/runtime/Errors.cpp#L168
<https://github.com/jckarter/swift/blob/master/stdlib/public/runtime/Errors.cpp#L168>
and
https://github.com/jckarter/swift/blob/master/stdlib/public/runtime/Errors.cpp#L204
<https://github.com/jckarter/swift/blob/master/stdlib/public/runtime/Errors.cpp#L204>
for the relevant runtime source code. cc'ing Greg Parker who probably knows
better exactly where these messages end up.
-Joe
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